The present invention relates to a method of producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous netting formed of a thermoplastic polymer material, wherein such a surface coating is provided on at east a part of the surface of the base layer.
Mineral fibre material is used, among other things, for thermal and acoustic insulation in a n umber of connections.
In order to increase the tactility of the mineral fibre material used during the handling and mounting thereof it may be coated with a surface layer, e.g. consisting of a non-woven sheet material of polymer fibres.
Furthermore, such a surface coating serves to reduce or eliminate the release of fibre wads or single fibres from the mineral fibre material to the surroundings before, during or after mounting.
Furthermore, a surface coating of the above-mentioned type imparts a considerably increased tensile strength to the mineral fibre element.
It is known to produce mineral fibre elements of the type mentioned in the introductory part by adhering a pre-manufactured, non-woven web material consisting of polymer fibres to the surface of a web-formed mineral fibre material by using a resin, such as phenol formaldehyde resin, as an adhesive, and by subsequently cutting the coated mineral fibre web so as to form individual mineral fibre matts.
Non-woven polymer fibre materials can be produced from thermoplastic polymers which, among things, are characteristic in being adhesive in melted state. In the production of non-woven fibre materials the adhesive effect can be used to bond the individual fibres together to form a coherent layer.
However, the prior art method suffers from several drawbacks.
In order to impart sufficient strength to the non-woven material so as to enable it to resist strains during the handling thereof and in particular during the application of the material onto the uneven surface of the mineral fibre material, the material used should have a surface weight of at least about 20 g/m.sup.2.
However, it is not necessary to use a surface coating having a surface weight of such a magnitude in order to obtain a functional coating, and hence the prior art method involves a certain waste of material.
Furthermore, the resin used for adhering the non-woven material implies an increase in the thermal value of the surface coated mineral fibre element, which is undesirable for fire safety reasons.
In addition, mineral fibre elements produced by the prior art method are relatively costly, which is partly due to the fact that non-woven polymer fibre materials are costly and partly that the method comprises at least two relatively difficult technical process steps, viz. 1) an even application of the adhesive onto the surface of the base layer and 2) mounting and pressing of the coating onto the surface.
Finally, it is strenuous and difficult to form a surface coating covering the entire surface of the base layer, i.e., both the upper side and lower side of the base layer and its edge surfaces, by use of the prior art method.
The object of the present invention is to provide a method of the type mentioned in the introductory part which is simpler than the prior art method and by which a mineral fibre element having improved properties can be obtained.